Coordinating adhesion mechanisms during brain morphogenesis

Ohio State University, The, Columbus OH

Investigators

Abstract

Animals and their constituent tissues are assembled from large numbers of cells, which are held together by specialized adhesion molecules. As the three-dimensional structure of embryos emerges in development, cell-cell adhesion regulates the coordinated changes in cell shape, and movement, as well as cell number. How cell-cell adhesion coordinates these cell properties during development is not well understood. The long-term goal of this research program is to understand how cell adhesion controls development using the vertebrate brain as a model. The Principle Investigator has previously found that two adhesion molecules (Protocadherin-19 and N-cadherin) appear to cooperate in early stages of brain development. Investigators will use time-lapse imaging of living zebrafish embryos to visualize the functions of Protocadherin-19 and N-cadherin during the formation of the embryonic brain. As both Protocadherin-19 and N-cadherin are members of larger families of molecules, the proposed studies will be broadly relevant to the mechanisms by which vertebrate animals are formed during development. The proposed research will provide a rich training environment at the graduate, undergraduate and high school levels, with exposure to state-of-the-art genetic tools, sophisticated imaging approaches and quantitative image analysis. During animal development, changes in cell number, cell shape and cell movement are coordinated to bring about the morphogenesis of complex three-dimensional tissues. Cell-cell adhesion is particularly important for morphogenesis, as it facilitates cell motility, maintains cell polarity and coordinates collective cell migration. Despite this central importance, relatively little is known about the mechanisms that dynamically regulate cell-cell adhesion during development. The classical cadherins (including N-cadherin) comprise a family of hemophilic cell adhesion molecules that are essential for vertebrate morphogenesis, and participate in a range of developmental processes. Protocadherins are a large family of molecules that are related to classical cadherins, although much less is known about their cellular and developmental functions. Previous work from this investigator's laboratory showed that Protocadherin-19 (Pcdh19) is involved in anterior neurulation in zebrafish, that it functions synergistically with N-cadherin (Ncad), and that Pcdh19 and Ncad interact in cis to form an adhesive complex. This interaction could provide a mechanism for dynamically switching between functional adhesive states within the cell, thus coordinating distinct adhesive systems during complex sequences of morphogenetic movements. The core objectives of this proposal are to: 1) understand how adhesion by Ncad and Pcdh19-Ncad coordinate collective cell behaviors during anterior neurulation, and 2) understand how these distinct adhesion mechanisms regulate actin dynamics during cell movements. To accomplish these objectives, the Principle Investigator and colleagues have established a zebrafish line mutant for pcdh19, as well as transgenic lines generated with ncad and pcdh19 promoters. These transgenic and mutant zebrafish lines will be used in conjunction with in vivo 2-photon time-lapse microscopy to dissect the functional significance of the Pcdh19-Ncad complex during development of the nervous system, and to determine how they influence actin dynamics during coordinated cell movements.